The invention is directed to an improved safety device for a power control on an engine.
In a known safety device for a power control system of a driving engine or motor, a driver and a control element are provided. In a normal operating state, the driver is actuated by an operating element and the control element is actuated by an actuator. To prevent the control element from assuming an unauthorized control position relative to the driver, the safety device is provided.
Three contact elements are provided on the control element. The first contact element is a wiper, which moves along a first contact path. The second contact element is also a wiper. The second contact element sweeps over a second contact path only in the idling range of the driving engine. In the partial-load range, the second contact element moves past the contact path; that is, it leaves the second contact path. For the third contact element, a third contact path is provided. The third contact path for the third contact element can be adjusted by a mimicking means in such a way that the third contact element touches the contact path only in the partial-load and full-load range. The third contact path for the third contact element in turn is put in contact with a regulating device, via a wiper that moves along a fourth contact path extending at angle. The third contact path for the third contact element is shorter than a free play between the control element and a clearance hook coupled to the driver.
The known safety device has several grave disadvantages. The second contact path for the second contact element does not extend over the entire length of possible motion of the associated second contact element. In other words, the second contact element sometimes travels over the contact path and sometimes is off it. No matter how thin the contact path for the second contact element is, there is still an at least small step at the beginning or end of the contact path. This step has to be overcome by the contact element. In long-term operation, this leads to damage of the second contact element. The step also wears over time, so that the beginning or end of the second contact path shifts over time, or in other words a state that cannot be defined precisely ensues. Furthermore, the third contact path for the third contact element must be pressed onto or lifted from the third contact element via a mimicking mechanism, which is not exactly simple to make. In pressing the third contact path onto the third contact element, or lifting it from it, increased friction arises between the clearance hook and a ramp incline carrying this hook. The action of pressing down and lifting off can also form sparks between the third contact element and the third contact path, which makes it likely that the service life of the third contact path will be shortened. Moreover, depending on the position of the control element relative to the driver, the third contact element also moves beyond the third contact path, so that damage and increased wear also occur at the end of the third contact path, between the third contact element and the contact path. For the above reasons in particular, accurate definition of the onset or end of contact between the second contact element and the second contact path and between the third contact element and the third contact path is not possible, so that in the course of the service life of the safety device, considerable shifting in the onset or end of contact with the contact paths must be expected.